Furnaces for carrying out chemical vapor deposition (CVD) and/or chemical vapor infiltration (CVI) are well known and are discussed for example, in U.S. Pat. No. 6,162,298 to Rudolph, the entire contents of which is hereby incorporated by reference. In such furnaces, process gas is introduced into a lower portion of a furnace where it passes through a gas preheating system and is heated before it enters the processing portion of the furnace.
Conventional gas preheating systems generally occupy a relatively large part of the lower portion of a furnace and reduce the amount of space in the furnace for holding materials to be processed. If the thickness of such conventional preheaters is reduced, however, gases may not be heated and mixed to an adequate degree before entering the furnace. The thickness of the preheating system therefore represents a tradeoff between the amount of usable space inside the furnace taken up by the preheating system and the ability of the preheating system to adequately preheat and distribute the gas before it is released into the furnace.
In addition, products to be processed in a CVD or CVI furnace are often placed or stacked on a pallet or other support for ease of handling, and this pallet with the products loaded thereon is then placed into the furnace. The height of the pallet further reduces the space available for products in the furnace.
It would therefore be desirable to provide a gas preheating system for a CVD/CVI furnace that preheats and distributes process gases in a satisfactory manner while taking up less space in a furnace than conventional gas preheaters, and, optionally, that can be used as a support or pallet for transferring work pieces to and from a furnace.